But after a little thought, I would argue that it's not deterministic. The whole design of our deterministic systems is to exclude any result but a desired target result. Our computers work because when we add 2 + 3, any result other than 5 is so unlikely that we can basically assume it will be.

Faults in modern processors are usually limited by design to a probability of 100 billion-to-1 or higher.

When we look at the fundamental (quantum) operations of the universe though: Everything is a probability. At the outset, we have Heisenberg Uncertainty Principle, which (loosely stated) is that we cannot observe quantum particles without affecting (changing the state) of those particles.

But about 80 years later, we find that HUP also interferes with a particle "knowing" if it is observed. So sometimes we can find out both momentum and position of a particle without affecting the particle at all, because the observation has a finite probability of occurring without affecting the observed particle.

Where one cannot predict the results of an interaction, it seems to me there is no determinism.

It's a case of quantum superposition of determinism/non-determinism. It will be whatever you measure it to be for however long you measure it that way with your notion that it must be one of two ways, depending on which one you think is the correct interpretation.

But that doesn't affect us practically since that won't occur for 1×101000years or so. In the meantime, there seems to be a lot of...flexibility. We could get there via Hoboken, Anchorage, Shanghai, or Timbuktu.

Of course, Heat death of the universe points out that this all could result in another universe being formed in 101056 years or so, so maybe even entropy isn't final. (That didn't render well in Discourse; try this: 10^(10^56)

I'm with non-deterministic, but we'll never be able to prove either position.

To the people randomly using the words "quantum mechanics": QM doesn't mean the universe is non-deterministic. It could mean we just don't get the laws underlying QM. And observer influence is totally irrelevant.

I'm pretty sure quantum physics has already proved (as much as it is possible to "prove" something) that the path of subatomic particles is nondeterministic as fuck.

However conflating this with your philosophical ideas of "free will" and whatnot is a huge fallacy. Brains are still machines, and people's actions and beliefs are still mostly predictable by looking at their experiences and education (and genetic structure, etc.). Deal with it.

Also this doesn't mean we have no responsibility for our actions either. I admit this concept is a bit complicated.

Xcode and clang have convinced me there is no way the universe is deterministic. If a compiler can fail to compile a project 22 times in a row and then succeed on the 23rd time with absolutely no changes anywhere, there's no way determinism is a thing.

However conflating this with your philosophical ideas of "free will" and whatnot is a huge fallacy. Brains are still machines, and people's actions and beliefs are still mostly predictable by looking at their experiences and education (and genetic structure, etc.). Deal with it.

But the brain machine is composed of quantum particles that you just said are non-deterministic....

Though I actually voted for deterministic, even though it requires a major breakthrough in quantum physics that may or may not exist or be possible.

It's possible that the universe would be deterministic IIF you could see the strings behind the scenes, but that you can't see those strings from within the system.

If you've ever wondered what the route to heat death looks like, wiki has you covered on that front too [spoiler]basically the fabric of the universe rips itself apart at smaller and smaller scales over longer and longer timeframes[/spoiler]:

While predictions of the future can never be absolutely certain, present understanding in various fields allows for the prediction of far-future events, if only in the broadest outline. These fields include astrophysics, which has revealed how planets and stars form, interact, and die; particle...

Xcode and clang have convinced me there is no way the universe is deterministic. If a compiler can fail to compile a project 22 times in a row and then succeed on the 23rd time with absolutely no changes anywhere, there's no way determinism is a thing.

Noun
matter (countable and uncountable, plural matters)
Substance, material.
(physics) The basic structural component of the universe. Matter usually has mass and volume.(physics) Matter made up of normal particles, not antiparticles. (Non-antimatter matter).A kind of substance.
vegetable matter
Written material (especially in books or magazines).
printed matter; He always took some reading matter with him on the plane.
(philosophy) Aristotelian: undeveloped potentiality subject to change and development; formlessness. Matter receives form, and becomes substance.
A condition, subject or affair, especially one of concern.
[quotations ▼]What's the matter?; state matters

An approximate amount or extent.
[quotations ▼]I stayed for a matter of months.

But the brain machine is composed of quantum particles that you just said are non-deterministic....

So is a rock, a car or a computer, but I can still predict what they will do with >99.999999999[lots of 9s]% probability of being right. Quantum systems behave almost-deterministically if they're big enough.

Unless of course there's something in that system that amplifies the quantum randomness, like the particle detector in the Schrödinger's cat thought experiment. Which could be true of neurons, but AFAIK we have no reason to believe this is likely.